Analysis and interpretation of fibre optic temperature data at the Polokwane Smelter

Abstract

The Polokwane Smelter operates a single sixin-line electric furnace, nominally rated at 68 MW. The smelter treats mainly Platreef, and UG2 concentrates from the eastern and northern limbs of the Bushveld Complex and smelts them to form slag, matte, and gas phases. The furnace operates with three matte tap-holes on the northern wall of the furnace and matte is tapped periodically from the furnace, with each tap being 25 to 35 minutes in duration. Two tap-holes are utilized per day, with one resting. A tap-hole is not utilized for more than two days in succession to ensure that it is not over-utilized and also to allow for any tapping channel refractory preventative maintenance.The matte tap-holes consist of copper cooling elements within which are refractories that contain the tapping channel. The hot face of the water-cooled copper tap-block is separated from the molten material by refractories. It is within, or on the surface of, the copper tap-blocks that the fibre optic technology was embedded. Due to the higher superheats of PGM matte compared to most other types of matte (Shaw et al., 2012;Nolet, 2014), the matte tap-holes are subjected to extreme process conditions which may render the furnace prone to failures. The wearing of these refractories introduces the risk of explosions should any matte come into contact with the copper block and then the cooling water channel.Fibre optic technology was installed strategically at the hot face and within the water-cooled copper tap-blocks and key watercooled copper coolers, with the intent to provide a more detailed and timely detection of temperature rises in the copper, refractory, and associated freeze-lining components on the hot face of the matte endwall, copper coolers, and the tap-block. Prior to the introduction of fibre optic technology, the methods of endwall condition monitoring were limited to the measurement of copper temperatures of the tap-block and cooper coolers by thermocouples installed at specific points, and the use of resistance temperature detectors (RTDs) that measure the change in cooling water temperature. The selection of fibre optics was made to provide a significantly higher density of sensors with an enhanced spatial resolution in comparison to the single conventional temperature measurements.Two types of fibre optic technology were installed in different copper tap-blocks and coolers, namely type A technology utilizing Bragg gratings and type B utilizing the Raman effect. The Bragg gratings reflect a wavelength of light that shifts in response to variations in Analysis and interpretation of fibre optic temperature data at the Polokwane Smelter by R.L. Sakaran, Q. van Rooyen, P.K. van Manen, and P.P. MukumbeTo help improve the monitoring of the matte tap-holes on the matte endwall to prevent failures, fibre optic temperature systems were installed on the six-in-line electric furnace at the Polokwane Smelter. This was done with the intent to provide more detailed and timely detection regarding the change in condition of the copper coole...